Table 1 Methodology for psychometric analysis of PCPCM-SC-FDCS

Structural validity

We conducted Rasch analysis to assess the structural validity of the PCPCM-SC-FDCS scale, examining unidimensionality, local independence, monotonicity, and overall model fit.

1. Unidimensionality: Standardized item-person fit residuals fall within the range of -2.5 to 2.5.

2. Local Independence: Q3 values are less than 0.37.

3. Monotonicity: The scalability coefficients of the items should be greater than 0.30 to ensure monotonicity in the measurement.

4. Model Fit: Infit and outfit mean squares fall within the range of 0.5 to 1.5.

Internal consistency

We assessed the internal consistency of the PCPCM-SC-FDCS scale by calculating Cronbach’s alpha and examining evidence for unidimensionality using PCA with the proportion of variance explained and the scree plot.

1. Cronbach’s Alpha: Values between 0.70 and 0.95.

2. Unidimensionality via PCA: The first principal component explains a substantial portion of variance (e.g., > 20%) and is supported by a clear “elbow” in the scree plot.

Reliability

We administered the questionnaire twice, 14 days apart, to the same cohort of patients enrolled in the family doctor contract service to evaluate test-retest reliability using ICC.

ICC was ≥ 0.70.

Criterion Validity

We evaluated the convergent validity of the PCPCM-SC-FDCS by comparing its scores to the widely adopted and validated Chinese version of the PCAT, currently the most classic and widely used instrument for assessing primary care functional features in mainland China.

The correlation with the PCAT was ≥ 0.70.